1. Field of the Invention
This invention pertains to cutting devices, and more particularly to apparatus for precisely cutting and stripping insulation from insulated electrical conductors.
2. Description of the Prior Art
Industry utilizes two basic types of stripping blades for high production cutting and stripping of insulation from insulated electrical conductors, the "die" type and the "V" type. In the die type design, a pair of knife blades form complementary halves of a counterbored hole and a smaller through hole. The two blades are closed over the insulation of a specifically sized elongated insulated conductor to penetrate and cut the insulation. The die type design possesses the advantage of having the cutting edges closely conform to the configuration of the conductor around the full periphery thereof. Further, in the die type design the leading edges of the mating blades butt together at the end of the cutting stroke. The butting action provides excellent depth control for the cutting edges, thereby preventing nicking of the conductor.
Despite their advantages, die type blades have some serious drawbacks. One disadvantage is that a pair of die blades can be used with only one size of insulated conductor. A set of die blades thus lacks flexibility for processing larger or smaller conductor sizes. A second drawback of die type stripping blades is that they lack satisfactory sharp edges completely around the circumference of the hole formed by the mating blades. As a result, mating blades tend to squeeze rather than cut the insulation, and the insulation to be stripped must be torn from the parent insulation. A third disadvantage of die type blades is that they have limited ability to accommodate off-center insulated conductors transported between the open blades. In many applications, wire guides are required to help gather the insulated conductor into the working area between the blade cutting edges.
The V type stripping blade overcomes many of the disadvantages of the die type blades. For example, a single pair of V type blades can cut and strip several sizes of insulated conductors. Another advantage is that the V type blades have sharp knife edges that slice cleanly through the entire circumference of the insulation rather than merely squeezing it. V type blades possess the further advantage of being capable of gathering offset insulated conductors to the cutting edges. An exemplary design of V type blades is shown in U.S. Pat. No. 4,577,405, which describes a blade having a compound processing angle. The compound angle blade combines the flexibility of being able to handle a range of insulated conductor sizes with a sharp edge around the entire cutting edge. In essence, the compound angle blade combines the circumferential contact of the die type blade with the versatility and gathering ability of the V type blade.
Despite the benefits of the single angle and compound angle V type blades, they nevertheless occasionally present a certain problem. That problem pertains to misaligned blades. Should the blades be skewed because of mounting misalignment in the tool holder or for other reasons, the blades do not close to create a perfect circle around the insulated conductor. Consequently, the blades are likely to nick or cut off strands of the conductor.
A beneficial characteristic of die type stripping blades is that the blades can be manufactured to reduce misalignment by forming them with mating fingers and notches, such as is shown in U.S. Pat. No. 2,844,056. The design of the blades of the U.S. Pat. No. 2,844,056 is not completely satisfactory, however. That is because the guiding fingers and notches are located at some distance from the insulation cutting edges. Consequently, even though the finger and notch portions of the blades may be accurately aligned and guide each other, such accuracy is not inherently present at the cutting edges. Accordingly, merely changing V type blades to adopt the finger and notch of the die type blade does not solve the V blade misalignment problem.
Thus, a need exists for V type stripping blades that precisely cut and strip insulated electrical conductors on a production basis.